"What do you need boy robes for?" inquires Madam Malkins.
"I'm sometimes a boy," the girl explains.
"What?"
"Look—"
"I had to badger him a lot before he explained that was how it actually worked, and then he said I'd probably go to his House."
"– So I'm not sure if the Deputy Headmaster told you and it's kinda public knowledge and it's probably something you should know, but, uh, we had a war?"
"It ended – not that long ago, main guy on the opposing side seems to be gone for good. Might mean there's some prejudice against Slytherin, more so than usual."
"'Main guy'? Like, a president or something? And what's Slytherin got to do with it?"
"It was more like a civil war. People don't like to say his name, there were at least rumours there was a curse on saying it, and he was– very Slytherin, in the stereotypical way, and a lot of his followers were too."
"Wwwhhhhhat exactly is the stereotypical way of being 'very Slytherin'?"
Anthony pauses, thinking, then says, almost as if he has a checklist: "Dark. Having some weird link to snakes of some kind. Typically hate muggleborns, or anyone who isn't pureblood. Sort of – uncaring about what people feel. Use bribery and extortion to get what they want, and they want to rule the world for the sake of having power."
"… I mean, partially because of the same guy – he was gone for a while and resurfaced just recently – but also the house traits are cunning and ambition, so you tend to get quite a few from there who try, uh, less horrible versions of that?"
"… I mean, if you have a group of people and it turns out a tenth of them joined 'the dark side', the group is probably going to get a stereotype?"
"No, but he had–" Anthony pauses, looks around, and then continues in a lower voice: "He had like thirty direct followers in his inner sanctum, they all had their families indoctrinated, pureblood Slytherin families have high numbers of Slytherins who then try to indoctrinate others, and there are large bits of the population who were sympathetic to his goal of killing off muggles and non-purebloods?"
Pause. "It sounds like they need someone like that, yeah, but depending on who else is there you might be at risk of – not literally – being eaten alive. Seeing as you're muggleborn."
"Yes well whatever I'm still gonna do it, and I'm gonna be better than all of them. I'll show them. I'll show them all!"
He laughs. "I'm pretty sure I can't either. But I don't plan on taking over Slytherin, so that's okay."